Heat exchanger for hot gas engines



sept, 7, 1954 H. DE BREY ETAL 2,688,228

- HEAT EXCHANGER FOR HOT GAS ENGINES Filed April 22, 1948 l 3 Sheets-Sheet l V INVENTORS HEINRICH DE BREY AND FRANCISCUS LAMBERTUS VAN WEENEN Sept. 7, 1954 [)5 E ETAL 2,,688,228

HEAT EXCHANGER FOR HOT GAS ENGINES Filed April 22, 1948 3 Sheets-Sheet 2 M ZO HEHNIRICH DE BREY AND FRANCISCUS LAMBERTUS VAN WEENEN Sept. 7, 1954 H. DE BREY ET AL HEAT EXCHANGER FOR HOT GAS ENGINES 3 Sheets-Sheet 3 Filed April 22, 1948 INVENTORS HEINRICH DE BREY AND FRAMCISCUS LAMBERTUS VAN WEENEN I I I Patented Sept. 7, 1954 UNITED STATES PATENT OFFICE HEAT EXCHANGER FOR HOT GAS ENGINES Application April 22,1948, Serial No. 22,607

Claims priority, application Netherlands June 6, 1947 1 Claim. 1

The invention relates to a heat exchanger comprising one or more walls, across which heat exchange takes place between the media on either side of these walls. According to the invention,

such a heat exchanger is characterized by the 1 In It being= in which formula (T medium-T wall) input (T medium-T wall) output of a channel u=the coefiicients of heat-transfer F=the surface area of the wall served by the medium;

w=the thermal capacity of the amount of medium flowing through a channel in each second.

T=the temperature,

all this in corresponding units.

(1).) The medium flowing through each of the systems is supplied to and/or discharged from these systems in parallel combination with the medium flowing through each of the other systems,

(c) The supply and/or discharge of the medium flowing through each of the systems takes place by maintaining a pressure difference between entry and exit, this pressure difference exceeding the pressure difference produced by the temperature increase in the channels themselves. If, owing to an appreciable temperature drop in the vanes, the wall temperature should not be identical everywhere, this temperature must be substituted in the above formula by the effective temperature of the wall of the channel, the term effective temperature being understood to mean the even temperature throughout the wall of the channel, which, under equal conditions as far as condition of flow and temperature of the cooling or heating agent at the entry of the channel are concerned, would produce the same mean temperature of the agent at the exit.

The heat exchanger according to the invention has the great advantage that it may be of considerably smaller size than the heat exchangers hitherto known and the heat transfer between the cooling agent and the medium to be cooled or between the heating agent and the medium to be heated is much intenser so that a smaller size sufiices for equal reduction or increase in temperature of the medium to be cooled or to be heated.

The heat exchangers hitherto known comprising vanes generally exhibit'a high temperature drop in the vanes, which affects heat transfer and results in low efficiency of the arrangement.

In the latter case efforts may be made to increase the speed of flow of the cooling or heating agent so as to reduce the temperature drop in the vanes. However, the resistance is thus increasedmaterially and this may lead to increase the distance by which the vanes are spacedapart, with the result that the wall to be cooled or heated comprises a smaller number of vanes. This results in a decrease in total surface area,

so that the vanes require to be made heavier, that is to say in the majority of cases, to be made longer in a radial direction. The whole arrangement is thus rendered heavier and occupies a larger amount of space, whilst again there is the disadvantage that the channel through which the cooling or heating agent passes may become excessively large, which involves a low speed of flow and, consequently, a high temperature drop in the vanes, so that the efiiciency of the entire arrangement is again affected.

Efforts might be made to increase the channel width in the case of excessive resistance by making the vanes thinner but this is inconvenient in view of the thermal conductivity of the vanes.

The above remarks with respect to the surfaces along which the cooling or heating agent passes also apply, mutatis mutandis, to the surfaces along which the medium to be cooled or heated flows.

According to the invention, the efficiency of the heat exchanger is found optimum between the above mentioned values of the natural logarithm of the cooling factor viz. 0.25 and 4; if this value is chosen to be lower than approximately 0.25, the effect of the cooling or heating agent is insuflicient; if chosen to exceed approximately 4, the flow resistance becomes excessive, whilst this high value does not contribute appreciably to the chiciency of the heat exchanger. The losses due to the high resistance of flow are higher than the small gain in heat exchange.

In order that the invention may be more clearly understood and readily carried into effect, it will now be described more fully with reference to the accompanying drawing, which in part shows embodiments thereof.

Fig. 1 is a vertical section taken on the line I-I of Fig. 2 of a hot gas engine of a displacer type having a heat exchanger embodying the present invention incorporated therewith,

Figs. 2 and 3 are horizontal sections taken on the lines II--II and III-III of Fig. 1, and

Fig. 4 shows another side elevation view of the hot gas engine.

Referring more particularly to the drawings and especially to Fig. 1 the hot gas engine in which the present invention is applied is provided with a cylinder I in which a displacer piston 2 and a piston 3 reciprocate with a constant phase difference. The displacer piston 2 is connected by a piston rod 4 to a crank of the crank shaft (not shown) while the piston 3'is also connected by a piston rod 5 to cranks of the same crank shaft. The space 6 above the displacer piston 2 is the hot space and this space is connected by means of the heater 1, regenerator 8 and cooler 9 to a space l between the displacer piston 2 and the piston 3, which space is the cold space. The hot gas engine is surrounded by a shell II which is at its inner side provided with fins l2 and at its outer side with a number of fins l3 which is also shown in Figs. 2 and 3.

The hot gas engine is further provided with a ring burner M, the flue gases of which flow through the ducts l to the channels between the fins l3. After the working medium flowing along the fins I2 is heated, a part of the flue gases flows through the channels l6 and into the channels I! while another part will flow directly into the channels I! and leave the hot gas engine through the ports l8. The air used is supplied through the duct I!) which is connected to the ventilator 20 driven by the hot gas engine. Due to the further difierence in pressures between the ventilator 20 and the atmosphere, the flue gases flow in the direction shown by the arrows in the drawings.

What we claim is:

A hot-gas engine comprising a cylinder and at least one piston movable therein, a heater, re-

generator and cooler associated with said engine so that the working medium moving from one portion of said cylinder to another portion thereof traverses said heater, regenerator and cooler, afirst plurality of elongate fins attached edgewise to said cylinder adjacent to said heater and cooler, said fins being in substantially parallel relationship with each other, a second plurality of elongate fins attached edgewise to said first plurality of elongate fins at the edges thereof remote from said cylinder, said second plurality of elongate fins being in substantially parallel relationship with each other and extending in a direction substantially perpendicular to that of said first plurality of fins, said first and second plurality of fins, respectively, comprising channels formed between adjacent fins having widths of approximately ,3 of the total length of either of the plurality of fins, the maximum value of said widths being 10 mms., the minimum value being 0.3 mm., while the natural logarithm of the cooling factor .k is between 0.25 and 4; inlet means connected into some of said channels of said second plurality of fins, outlet means connected into other of said channels of said second plurality of fins, whereby said working medium flowing through said some of said channels moves in parallel with said working medium flowing through said other of said channels but in substantially opposite directions and means for maintaining a pressure diiference between the supply and discharge of said working medium flowing through said inlet and outlet means, respectively, said pressure difference exceeding the pressure difference produced by the increase in temperature in said channels themselves.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 871,797 Green Nov. 26, 1907 981,733 Wolke Jan. 1'7, 1911 1,389,780 Peck Sept. '6, 1921 2,369,993 Turner Feb. 20, 1945 2,406,551 Lucke Aug, 27, 1946 2,535,669 Clay Dec. 26, 1950 FOREIGN PATENTS Number Country Date 118,369 Australia Apr. 11, 1944 370,183 Germany Aug. 0, 1920 

